<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>4.天气案例_监视属性_简写</title>
    <!--  引入Vue  -->
    <script type="text/javascript" src="../js/vue.js"></script>
</head>
<body>
    <div id="root">
        <h2>今天的天气是{{info}}</h2>
        <button @click="changeWeather">切换</button>
    </div>
</body>

<script type="text/javascript">
    const vm = new Vue({
        el: '#root',
        data: {
            isHot: true
        },
        computed: {
            info() {
                return this.isHot ? '炎热' : '寒冷'
            }
        },
        methods: {
            changeWeather() {
                this.isHot = !this.isHot
            }
        },
        watch: {
            //正常写法
/*            isHot: {
                //初始化时让handler调用一下
                // immediate: true,
                //深度监视
                // deep: true,
                handler(newValue, oldValue) {
                    console.log("isHot 被修改了 ", newValue, oldValue)
                }
            }*/

            //简写
/*            isHot(newValue, oldValue){
                console.log("isHot 被修改了")
            }*/
        }
    })

    //正常写法
/*    vm.$watch('isHot', {
        //初始化时让handler调用一下
        // immediate: true,
        //深度监视
        // deep: true,
        handler(newValue, oldValue) {
            console.log("isHot 被修改了 ", newValue, oldValue)
        }
    })*/


    vm.$watch('isHot', function (newValue, oldValue) {
        console.log("isHot 被修改了 ", newValue, oldValue)
    })

</script>
</html>